Our goal is to identify molecules involved in signalling during mammalian development, especially during the development of the central nervous system (CNS). We are taking two complementary approaches. In the first, we are investigating the developmental roles of neuropeptides, known intercellular signalling molecules. In the second, we are cloning genes defined by murine mutants affected in CNS development As signalling molecules, neuropeptides are well characterized structurally but knowledge of their functional roles, especially in development, remains fragmentary. The data for their involvement is largely circumstantial, based on their occurrence at ectopic sites (relative to their sites of expression in the adult) in late stages of development. We have recently introduced a knockout allele of the somatostatin (SST) gene into the mouse germline and are analyzing its role in early embryonic development. To extend our study of SST in development, we have isolated genomic clones of the known SST receptor genes and are introducing knockout alleles of these in the mouse germline. Finally, to extend our work to other neuropeptides, we have begun a systematic description of neuropeptide expression from the earliest stages of development. In our second approach, we are isolating genes defined by mutations affecting discrete aspects of cerebellum development. Previously we had assembled yeast artificial chromosome (YAC) clones covering the 1.5 Mb of human chromosome 21 containing the human homolog of the weaver gene. We have produced large (6-10 fold coverage) genomic reference cosmid libraries from all of these YACs. We have screened these for sequences expressed in the developing cerebellum, and have identified 17 independent, novel genes. We are now analyzing these candidates for the weaver gene.